A. Regulation of Expression of the HoxA7 Gene. Work has continued on the description of the promoter region of HoxA7 using CAT reporter constructs and expression in NIH 3T3 cells. Deletions from the 5'- and 3'-sides of the promoter region provided further evidence for the presence of positive and negative regulatory elements controlling HoxA7 transcription. B. GTP Binding to HPr. The phosphocarrier protein HPr of the E. coli phosphoenolpyruvate:sugar phosphotransferase system binds GTP. A large collection of HPr mutant proteins provided a basis for mapping the topology of interaction of GTP with the protein. C. Crystal Structure of HPr from Mycoplasma. X-ray diffraction analysis was used to solve the structure of the protein, which was shown to exhibit an open-faced beta-sandwich topology. D. Structure-function Analysis of Enzyme I. Enzyme I from the E. coli phosphoenolpyruvate:sugar phosphotransferase system transfers a phosphoryl group specifically to HPr from E. coli and not to the acceptor proteins from other bacterial species. A recombinant form of the amino terminal domain of Enzyme I exhibits relaxed specificity for phosphoryl transfer to HPr. E. Chromosomal Mapping of Sugar Transport Genes of Mycoplasma. The unique arrangement of separate operons for the gene encoding HPr and those encoding Enzymes I and IIA of the phosphoenolpyruvate:sugar phosphotransferase system was further analyzed by chromosomal mapping. The two operons are located at opposite ends of the chromosome. F. Phosphate-dependent Regulation of Adenylyl Cyclase and Phosphodiesterase Activities. In intact cells of E. coli, inorganic orthophosphate stimulates the activity of adenylyl cyclase and inhibits the activity of cyclic AMP phosphodiesterase. A model is proposed for phosphate-dependent regulation of cellular cyclic AMP levels by a dual mechanism.